In a new book (Water, Race and Disease, MIT Press 2004), Werner Troesken analyzes the growth of water pollution control efforts in the early 20th century and finds that public water and sewer services for African Americans grew even under Jim Crow. From the MIT Press blurb: "Arguing that in this case, racism led public officials not to deny services but to improve them -- the only way to "protect" white neighborhoods against waste from black neighborhoods was to install water and sewer systems in both -- Troesken shows that when cities and towns had working water and sewer systems, typhoid and other waterborne diseases were virtually eradicated. This contributed to the great improvements in life expectancy (both in absolute terms and relative to whites) among urban blacks between 1900 and 1940."

EH.NET has an excellent review, not yet on their site.